Heat 2 tsp of the oil in a non-stick frying pan over medium heat. Add onion and cook, stirring, for 5 mins or until softened. Add carrot and beetroot and cook for 2 mins. Add curry paste and cook, stirring, for 1 min until aromatic. Set aside to cool completely.
Process bean mix and coriander in a food processor until coarsely chopped. Place onion mixture, bean mixture and breadcrumbs in a bowl. Use hands to mix until combined. Add salt & pepper to season as desired. Shape into 8 flat patties.
Heat remaining oil in a large frying pan over medium-high heat. Add patties and cook for 2 mins each side until golden. Transfer to paper towel to drain.
Top roll bases with tzatziki, spinach, patties, cucumber and herbs. Sandwich with roll tops.